well, you can change the temper of the blade...meaning it will get too soft to hold a good edge.
This is a chart that demonstrates...the specifics of course depend on the steel composition.
Temper Colors and Steel Hardness : anvilfire.com
Honestly though, I think 1000rpm on a bench buffer about the same than 5000 on a dremel. What matters isn't rpm, but edge speed for heat buildup and speed of work. Increase the radius/diameter by 2 times, and the diameter increased by 2x. And therefore the edge speed at the same RPM increases by the same multiple.
I have yet to really try a dremel on my razors though...busy trying to learn the art of the straight razor shave...ok...I really haven't sent by razor to be honed yet...but soon.